The subject invention relates to data communications and more particularly to a method and apparatus for increasing data transmission efficiency in networks employing turnaround transmission through a combination of terrestrial and satellite facilities. The disclosed embodiment relates to a system employing modems transmitting in a half duplex mode through telephone line and satellite facilities.
In such systems transmission delays on the order of 700 milliseconds or greater may be encountered. Such delays allow for undesirable generation of echoes which can interfere with data transmission. In the prior art, it has been the custom to disallow data transmission for extended periods necessary to assure noninterference by echoes. This has been accomplished by squelching the modem receiver for a fixed period of time, regardless of the actual transmission delay. Such delays introduce serious inefficiencies in data transmission capacity. The prior art has also been unable to cope with the problem of spurious echoes in multiple satellite environments.